Ophiactis lymani Ljungman, 1872

Alitto, Renata A. S., Bueno, Maristela L., Guilherme, Pablo D. B., Domenico, Maikon Di, Christensen, Ana Beardsley & Borges, Michela, 2018, Shallow-water brittle stars (Echinodermata: Ophiuroidea) from Araçá Bay (Southeastern Brazil), with spatial distribution considerations, Zootaxa 4405 (1), pp. 1-66 : 49-51

Ophiactis lymani Ljungman, 1872

( Fig. 17 )

Type locality. Salt Island , British Virgin Islands.

Maximum size. dd up to 5 mm ( Paim et al. 2015).

Material examined. 183 specimens (dd: 0.6–2.9 mm) from subtidal: ZUEC OPH 2156, St. XXII, 3 spms; ZUEC OPH 2175, St. 71, 3 spms; ZUEC OPH 2178, St. XXII, 15 spms; ZUEC OPH 2183, St. 71, 10 spms; ZUEC OPH 2185, St. XXI, 31 spms; ZUEC OPH 2188, St. XXII, 1 spm; ZUEC OPH 2204, St. XXII, 52 spms; ZUEC OPH 2254, St. XXVII, 2 spms; ZUEC OPH 2258, St. XIX, 12 spms; ZUEC OPH 2267, St. 145, 3 spms; ZUEC OPH 2279, St. XXVI, 35 spms; ZUEC OPH 2291, St. 145, 6 spms; ZUEC OPH 2292, St. XXVII, 1 spm; ZUEC OPH 2328, St. 9H, 1 spm; ZUEC OPH 2348, St. 20H, 5 spms; ZUEC OPH 2354, St. XXXIV, 2 spms. From rocky shore in a sponge: ZUEC OPH 2437, St. 14C, 1 spm.

Description. Disc: (dd: 1.5 mm) circular, covered by large and irregular scales, approximately eight between the centrodorsal and the edge of the disc. Radial shields three times as long as wide, united distally and separated proximally by one triangular scale. Delicate spines sparse on disc ( Fig. 17A ). Ventral interradius covered by small scales with some spines. Bursal slits broad ( Fig. 17B ). Oral shields diamond-shaped, as long as wide. Adoral shields broadened distally and separated proximally. One lateral oral papilla. One rectangular apical papilla ( Fig. 17C ).

Arms: typically hexamerous, occasionally pentamerous. Dorsal arm plates triangular fan-shaped, twice as wide as long and not contiguous ( Fig. 17D,F ). Ventral arm plates pentagonal with distal edge concave and not contiguous ( Fig. 17E,G ). One tentacle scale. Three blunt, denticulate arm spines. Distal segments with serrated, hooked spines ( Fig. 17D,E ).

Lateral arm plates ( Fig. 17H,I ): general outline: ventral portion projecting ventro-proximalwards; ventro-distal tip not projecting ventralwards. Outer surface ornamentation: trabecular intersections protruding to form knobs larger than stereom pores on small part of outer surface. Outer proximal edge: surface lined by discernible band of different stereom structure, restricted to central part; without spurs; central part not protruding; surface without horizontal striation. Spine articulations: on same level as remaining outer surface, middle spine articulation larger; distance between spine articulation increasing dorsalwards. Lobes simply separated, equal-sized; lobes parallel, bent, and tilted orientation; stereom massive; sigmoidal fold absent. Inner side, ridges and knobs: dominated by two separate central knobs; without additional dorsal structure on inner side; perforation on inner side.

Vertebrae: zygospondylous of universal type and non-keeled. Proximal side of vertebrae dorsally without large groove on the dorsal-distal muscular fossae ( Fig. 17J ). Zygocondyles nearly parallel and zygosphene fused with pair of zygocondyles ( Fig. 17K ). Dorso-distal muscular fossae transformed distalwards projecting far from distal edge of zygocondyles ( Fig. 17L ). Zygosphene projecting beyond ventral edge of zygocondyles with projecting part longer than zygocondyles ( Fig. 17M ).

Taxonomic comments. O. lymani may be easily confused with O. savignyi ( Hendler et al. 1995) particularly young specimens. There are differences in the arm plates of these two species: i) the trabecular network protruding to form knobs larger than stereom pores on small part of outer surface of lateral, dorsal, and, ventral arm plates in O. lymani while in O. savignyi the knobs are present on most of outer surface of lateral, dorsal, and, ventral arm plates; ii) the number of spine articulations are perfectly visible on lateral arm plates—three in O. lymani and five to six in O. savignyi . We believe that our descriptions of arm ossicles could help the delimitation of these species. Three arms spines were observed in all specimens in this study. However, larger specimens (5 mm dd) may have four arm spines ( Borges & Amaral 2005; Paim et al. 2015). Due to asexual reproduction, O. lymani is often found with arms of different sizes, usually three smaller arms and half of the disc, indicating recent fission ( Paim et al. 2015). O. lymani is also similar to O. brasiliensis , however, the latter differs in having radial shields more broadened distally and acute angle proximally and, the dorsal arm plates are oval ( Manso 1988).

Remarks. It was the most abundant species in our study (27% of brittle stars) and 80% of the specimens were in some stage of regeneration ( Hendler et al. 1995). The high incidence of fission in O. lymani may be an alternate reproductive strategy when low salinity slows gonadal maturation ( Lima et al. 2013). This could explain the high number of regenerating specimens in Araçá Bay. However this hypothesis needs to be tested based on data of salinity and rainfall patterns of the region ( Alitto et al. 2016). O. lymani is often associated with seagrass ( Lima et al. 2013), bryozoans ( Morgado & Tanaka 2001) and sponges ( Padua et al. 2013). It may also occur on sand and muddy bottom ( Manso et al. 2008; Pires-Vanin et al. 2014). O. lymani was sampled from sand (medium sand) and rubble bottom with a dredge (89% of spms), van Veen grab (10% of spms) and multicorer (1% of spms).

Distribution. Circum-tropical and circum-subtropical. In Brazil, it has been recorded in Tropical Atlantic (realm), Tropical Southwestern Atlantic (province): Northeastern Brazil ( Lima-Verde 1969; Magalhães et al. 2005; Neves et al. 2007; Gondim et al. 2008; Manso et al. 2008; Lima & Fernandes 2009; Paim et al. 2015), Trindade and Martin Vaz Islands ( Tommasi & Aron 1988). Temperate South America (realm), Warm Temperate Southwestern Atlantic (province): Southeastern Brazil ( Borges et al. 2002; Capítoli & Bemvenuti 2004; Borges & Amaral 2005; Netto et al. 2005; Oliveira et al. 2010).

From intertidal up to 600 m depth ( Alvarado & Solís-Marín 2013). The present study samples occurred at depths ranging from 19 to 21.5 m.

Selected references. Ljungman (1872): p. 629; Tommasi (1970): p. 22, fig. 14; Madsen (1970): p. 208, fig. 34; Albuquerque (1986): p. 138, fig. 23a–c; Borges & Amaral (2005): p. 249, fig. a–d; Manso et al. (2008): p. 187, fig. 14a,b; Paim et al. (2015): p. 9, fig. 6a–c [as Ophiactis lymani ]; Borges et al. (2002): p. 37, fig. 21c,d [as Ophiactis savignyi ].

Figures

FIGURE 17. Ophiactis lymani ZUEC OPH 2258 (2.9 mm dd). (A) Dorsal view.(B) Ventral view. (C) Detail of the oral view. (D) Detail of dorsal arm. (E) Detail of ventral arm. (F) Dorsal arm plate. (G) Ventral arm plate. (H-I) Lateral arm plate. (J) Vertebra—proximal surface. (K) Vertebra—distal surface. (L) Vertebra—dorsal surface. (M) Vertebra—ventral surface. Abbreviations: ads: adoral shields; ap: apical papilla; as: arm spine; bs:bursal slits; d: dorsal; dap:dorsal arm plate; ddi:dorsodistal; ddmf: dorso-distal muscular fossae; di: distal; dp: dorso-proximal; ds: disc spine; lap: lateral arm plate; lop: lateral oral papilla; os: oral shields; p: proximal; rs: radial shields; ts: tentacle scale; v: ventral; vap: ventral arm plate; vdi: ventro-distal; vp: ventro-proximal; zd: zygoscondyle; zp: zygosphene. Stereomicroscope photos: (A)–(E), scale bar equal to 0.5 mm. SEM photos: (F)–(M), scale bar equal to 100 µm.